ANALYSIS & OPINION

How aerospace helps shape simulation software

In his final report from the European Altair Technology Conference (EATC), Robert Roe discusses the aeronautical industry’s role in developing simulation technology

Increasingly complex demands on models and associated software, coming from the aeronautical industry, are leading not only to some of the most complex simulations in industry but also to new tools being integrated into established software platforms.

The European Altair Technology Conference (EATC), held in Munich at the end of June, demonstrated the complex models used in aeroplane design – as they move to a fully integrated simulation driven design process.

‘To have a great product we have to invest in advanced technologies – such as advanced non-linear simulation,’ was how Jack Yan, numerical simulations engineer at Airbus started his keynote address.

Air travel is a massive business and Airbus has managed to obtain a large share of that market -- an A320 takes off or lands every 2.5 seconds and this type of plane has carried more than seven billion passengers since 1988.

Keeping up with competitors in an industry where you cannot afford to have a product fail means getting it right the first time. This has led to the integration of highly accurate simulations into the design process, from concept through to major static tests.

Yan said: ‘The A350 will have a new design, for step-changing economic efficiency for our customers. It will have an airframe with advanced materials – 53 per cent of which will be made out of composites. It will have state-of-the-art aerodynamics, simple and efficient systems and the latest generation of engines.’

It is easy to make bold claims about a product’s performance but as Yan said: ‘We have to match the drive to have an advanced airframe – with advanced numerical simulation of that airframe.’

Simulation of an aircraft in the design phase is not a new concept. ‘Numerical simulations have been around within Airbus for the past 15 years,’ said Yan but now they are being increased in complexity to the point that would not have been possible just a few years ago without some of the most powerful HPC resources in the world.

Yan said: ‘Our main responsibilities are to support the design and certification of our aircraft, understanding and resolving any in-service issues with our products and mitigating risks through major static tests.’

Major static tests are full-scale tests of the aircraft’s structure, which includes both of the wings and the fuselage. This also includes a second test for the nose section: ‘These are the most important tests for the structural community within Airbus,’ said Yan.

Non-linear simulations are also used to understand structural behaviour and support method development. Furthermore they are used to predict damage and failure.

However, non-linear simulations are only part of the picture, Yan said: ‘Advanced numerical simulations are still a very small part of numerical simulation as a whole within Airbus.’ He explained that they also use a number of other tests, including: vulnerability testing, which deals with impacts and impact related damage; thermal analysis; optimisation; multi-body simulation; and linear GFEM.

The goal at Airbus is to ‘create a single fully integrated simulation-driven design process’. He explained that they are developing simulation to the point where it is implemented from ‘conceptual design, to detailed design, all the way to the certification of the aircraft and finally to the continued development of the aircraft.’

The teams at Airbus have identified three major bottlenecks that must be overcome, if fully integrated simulation is to be achieved. The first is the ‘misconception of capability’ said Yan. He explained that sometimes engineers ‘think that we are a black-box tool – if you just put in some inputs and you get the results – and that is not necessarily true.’

The second Yan described as the ‘perception of high cost’ which ties in neatly with the third bottleneck ‘the cost of modelling.’

Yan said: ‘Keep in mind that up to 50 per cent of the cost of a project can go into the model building, within that time we are not adding any value to the business. This is because in the aeronautics industry we have to build a lot of our modelling tools in quad and hex elements rather than tet elements that my colleagues in the automotive industry use. That makes auto-meshing a lot less reliable for us and that means that we have to mesh parts manually.’

The culmination of this work on numerical simulation has led to the creation of the Virtual Full Scale Test model (ViFST), used to support the A350 wide body major static tests.

The ViFST is the most comprehensive and detailed model ever created at Airbus. It was used for the major static tests and as such simulated both wings and the fuselage in unprecedented detail. Yan went as far as saying: ‘A model of this size, complexity, and fidelity has never been attempted before in numerical simulation.’

It consists of more than 15,000 meshed parts with every ply defined. It has more than 10,000,000 elements and more than 65,000,000 degrees of freedom. ‘These elements are not reduced integration; they are full integration elements,’ said Yan.

In order to complete this model and reduce the implications of the bottlenecks identified by Airbus, the company worked closely with Altair to develop tools that have now been integrated into the HyperWorks software platform. These tools are the mid-surface mesh mapper and the composite mapping tool.

Yan said: ‘Let’s say that you are given a task to build an FE model of a metallic wing rib. Usually these ribs are made from 2D elements with simplified geometry. For any given wing, there can be anywhere from 24 to 57 of these, and all of them are unique so you cannot use the same mesh.’

In the past the company would complete these tasks manually, inserting the data into the CAD model, fixing the geometry as they went and then meshing it. After that they would assign varying thicknesses to the rib. ‘As you can imagine, this is a very time consuming task,’ commented Yan.

Yan said: ‘Today with the mid-surface mesh mapper, this can be done relatively easily and quickly.’

The mid-surface mapper functionality is encapsulated by a very simple user interface on one window within HyperWorks. ‘All the engineer has to do is press start and wait for HyperWorks to do their job for it. You can also visualise what you have done by rendering the thickness assigned to different elements’ said Yan.

Yan commented: ‘You have taken a task that took an experienced HyperMesh user possibly hours to do, and brought it down to a couple of seconds.’

‘Now this tool works very well with metallic components, but what if you have a composite component-- 53 per cent of the A350 is made out of composites?’ said Yan.

This is where the other tool created through the collaboration with Altair -- the composite mapping tool --comes in.

Yan said: ‘You were given the task of producing an FE model of a composite door frame.’ In the past this again would have been completed manually. The team would have to ‘convert the concept ply data from the CAD and create shell sections and then reassign them manually onto this component, again very time consuming,’ said Yan.

Yan said: ‘What we can do today is read the composite ply data directly from the CAD model and HyperWorks creates all the entities that you need to build this model.’

The data can also be visualised, producing data on individual plies and see where they are on your model – ‘something we could not do in the past. You will now also be able to visualise the ply stacks and the ply directions which helps us check our work a lot more effectively,’ said Yan.

These tools have helped to reduce the cost of model building significantly; however there is another benefit to these tools and that is it allows more users with less experience of HyperWorks toolsets to be involved in the design process. ‘That opens up a whole new pool of resources for us,’ said Yan.

Yan said: ‘These tools actually helped us to complete the VifST model on time, which meant that we were able to successfully de-risk the major static test of the A350.’ He went on to explain that this in turn helps to keep the massive project on target. With a successful major static test, Airbus was able to achieve first flight of the A350 – which means that the company will be able to deliver this aircraft to the airlines on time. This not only benefit however, the company has also made its own tools more intuitive and easier to use, reducing the misconception of capability.

There is still work to be done to improve the model however, as Yan stated in his closing remarks. ‘We must make model-building a more economical, reliable and repeatable aspect of numerical simulations – this means we need to implement improvements such as batch meshing. We also want our tools to be more intelligent, meaning that we want them to be intuitive, easy to learn and able to guide users to an appropriate solution. And I think we have solved some of that through the new HyperWorks interface.’